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Abstract Staphylococcus aureus (S. aureus) is known as a food-borne pathogenic bacteria that is difficult to deal with, especially in a biofilm. An appropriate and effective agent against S. aureus is urgently needed, especially due to the high pathogenicity of S. aureus within biofilms. This paper aims to synthesize Ag 3 PW 12 O 40 nanoparticles (AgWPA-NPs) and investigate their antimicrobial activity and mechanism against S. aureus. N-phenyl-1-naphthylamine (NPN) uptake and membrane potential assays showed that AgWPA-NPs damaged the structure of the cell membrane. Furthermore, the results of crystal violet staining and fluorescence microscopy indicated that AgWPA-NPs were remarkably efficient at suppressing the formation of S. aureus biofilms. Furthermore, real-time PCR analysis showed that the expression of the biofilm-related genes, icaA , sarA and cidA , was downregulated. Taken together, these results suggest that AgWPA-NPs have the potential to be an anti- S. aureus biofilm agent. Highlights • AgWPA-NPs damaged the structure of S. aureus cell membrane. • AgWPA-NPs inhibited growth of S. aureus in biofilm and eliminated S. aureus biofilm. • AgWPA-NPs inhibited the biofilm-related genes and expression of SEA and SEB. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus ( S . aureus ) is the leading cause of a broad range of human infections and associated with food poisoning worldwide. Nisin can be considered as a natural preservative and is widely used by the food industry. However, resistance of nisin has been reported in several species of bacteria. Identification of antibacterial agents that are synergistic with nisin is a method of minimising resistance to nisin. Cinnamaldehyde (CA), a well-studied essential oil isolated from cinnamon bark, has been reported to exhibit a broad spectrum of antimicrobial activity across a wide range of microorganisms. Previous studies have demonstrated that CA could be used in the food industry due to its active antibacterial activity and its safety. In this study, the synergistic antibacterial activity in vitro of nisin and CA against 13 food-borne isolates of S. aureus and S. aureus ATCC 29213 were evaluated by a checkerboard assay. The FICI values of nisin combined with CA ranged from 0.1875 to 0.375, which demonstrated a synergistic effect. The positive interactions were verified using the challenge tests in pasteurized milk and agar diffusion assays. The LIVE/DEAD BacLight experiment and scanning electron microscope (SEM) assay were also performed to distinguish the intact and damaged both of cell walls and membranes with the compounds, the combination group displayed stronger damage both of cell wall and cell membrane than when nisin or CA was used alone. These findings indicated that the combination of nisin and CA could not only be used as a promising naturally sourced food preservative but also to reduce the problem of bacterial resistance. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus ( S. aureus ), a major food-borne pathogen, causes disease in mammalian hosts by producing a wide variety of exoproteins, such as α-hemolysin and staphylococcal enterotoxins. Tea tree oil (TTO), an essential oil, has broad-spectrum antimicrobial activity. The objectives of this study were to evaluate the inhibitory effects of TTO on S. aureus growth and on α-hemolysin, enterotoxins A and B production. In this study, the effect of TTO on S. aureus growth in laboratory medium and pasteurized milk was determined by time-kill assays. Treatment with half of minimal inhibitory concentration (MIC) of TTO demonstrated very little or no reduction in numbers of viable ATCC 29213 cells; however, 1 × MIC of TTO reduced the viable cell count more noticeably, and 2 × MIC of TTO demonstrated an even greater reduction in the viable cell count, both in TSB and milk. The influence of TTO on enterotoxins was determined by real-time reverse transcriptase-PCR (real-time RT-PCR), a hemolysis assay, Western blot and a tumor necrosis factor alpha (TNF-α) assay. The real-time RT-PCR results revealed that the transcription of genes encoding α-hemolysin, staphylococcal enterotoxin A (SEA) and staphylococcal enterotoxin B (SEB) were down regulated after S. aureus was exposed to TTO (0.0625 mg/mL-0.5 mg/mL). The hemolytic assay showed that S. aureus hemolytic activity was inhibited by subinhibitory concentrations of TTO (0.0625 mg/mL-0.5 mg/mL). The Western blot assay identified that the production of the three virulence factors was inhibited by TTO (0.0625 mg/mL-0.5 mg/mL). Moreover, the enzyme linked immunosorbent assay (ELISA) demonstrated that TNF-α production was suppressed by TTO treatment in RAW264.7 cells stimulated by S. aureus supernatant containing staphylococcal enterotoxins (SEs). [ABSTRACT FROM AUTHOR]

The bacterium Staphylococcus aureus is most often recognized as a common cause of food poisoning. S. aureus colonization in humans can cause serious infections, toxinoses and life-threatening diseases. Nisin is a bacteriocin that has been extensively used as a natural preservative in the food industry, but the overall transcriptional response of S. aureus to nisin has not been well characterized. We used whole-genome DNA microarrays of S. aureus to determine the global transcription profile triggered by nisin treatment in S. aureus . In response to nisin treatment, a total of 601 genes were differentially regulated; transcription of 327 genes was up-regulated, and transcription of 274 genes was down-regulated. Various transporter genes showed elevated transcription, including genes involved in capsule polysaccharide (CP) synthesis, cell-wall synthesis, nucleic-acid and nucleotide metabolism as well as genes encoding urease, transport/binding proteins, and lipoproteins. To our knowledge, this transcriptome analysis provides the first insights into the transcriptional response of S. aureus to nisin challenge and enables exploration of the mechanisms of nisin antimicrobial activity toward S. aureus . The findings suggest that nisin regulates multiple desirable targets which could be further explored in the development of new food preservatives to avoid the contamination of S. aureus in food processing and storage. [ABSTRACT FROM AUTHOR]

Nisin has been widely used as a natural preservative in foods including dairy products, but the emergence of the nisin-resistant strains could compromise its use to control food-borne pathogens. It has been reported that coenzyme Q (CoQ) is a powerful antioxidant, but a small number of studies have described the antibacterial activity of CoQ. One of the most abundant forms of CoQ is CoQ10. CoQ0 is chosen for this study, which is the water-soluble homolog of CoQ10. In the present study, the in vitro interaction of nisin and CoQ0 against 15 food-borne isolates of Staphylococcus aureus was assessed using a checkerboard microdilution method. Synergism was observed in strains tested, the FICI values ranging from 0.25 to 0.375. No antagonistic interaction between nisin and CoQ0 occurred. The positive interactions were verified confirmed using the time-killing test and agar diffusion assay. Our discovery of efficacy of combining nisin with CoQ0 might pave the way for a novel solution for spoilage problem in food industry and provide an alternative approach to overcome antimicrobial drug resistance. [ABSTRACT FROM AUTHOR]